In this application, we propose to continue the successful Washington University Training Program in academic investigative pediatric gastroenterology, nutrition, and hepatology, by providing a two year immersion in research to physicians and scientists who wish to focus their training in areas relevant to these fields. The Program utilizes three tracks to leverage institutional, Department, and Division strengths, and pursue new concepts in investigative pediatric gastroenterology: Track 1 Microbial- Host interactions in the Gastrointestinal Tract (Faculty Mentors: Berg, Gordon, Mardis;Miller, Tarr, Wang) is formed in consideration of provocative data regarding host - flora interactions, strong pathogenesis and pathogen discovery groups at Washington University, the Washington University Genome Sequencing Center, and the Center for Genome Sciences and its gnotobiotic facility, which enables studies of host-microbial mutualism in the developing gut;Track 2, Cellular and Molecular Biology of the Developing Gastrointestinal Tract (Faculty Mentors: Davidson, Dieckgraefe, Ferkol;Gitlin, Heuckeroth, Holtzman, Li, Mecham, Milbrandt, Muglia, Rubin, Rudnick, Schwartz, Stenson), exploits this institution's strengths in modern biologic study of health and disease, and includes as mentors investigators who represent the traditional core of this Program;Track 3, Translational Biology of the Gastrointestinal Tract (Faculty Mentors: DeBaun, Ferkol, Klein, Shepherd, Tarr) avails itself of expanding capacities (including recent institutional T32, K12, and K30 Awards) at Washington University to study disease processes in human hosts and populations. This Program will continue to use extensive oversight of trainees and embedded mentoring and evaluation mechanisms, and Washington University's broad and deep research base, to train leaders in pediatric academic gastroenterology, nutrition, and hepatology.